A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces (a disk may also be referred to as a platter). When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head which is positioned over a specific location of a disk by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head and the surface of a magnetic-recording disk must be tightly controlled. An actuator relies on suspension's force on the read/write head to provide the proper distance between the read/write head and the surface of the magnetic-recording disk while the magnetic-recording disk rotates. A read/write head therefore is said to “fly” over the surface of the magnetic-recording disk. When the magnetic-recording disk stops spinning, a read/write head must either “land” or be pulled away onto a mechanical landing ramp from the disk surface. Because the read/write head flies so close to the surface of the magnetic-recording disk, the components within the HDD may be sensitive to moisture, contaminants, and other impurities and imperfections within the protective enclosure of the HDD.
Modern HDDs have a very thin overcoat and lubricant layers as well as very thin or even absent protective layers on the read and write heads. To protect high performance drives against corrosion and other negative outcomes, it is desirable to control the relative humidity within the drives. This has been accomplished in certain HDDs through the use of desiccants.
During either the manufacturing of a HDD or a long storage time of the HDD in a high humidity environment, the desiccant within the HDD can absorb a large quantity of moisture. When the HDD is powered on, the desiccant may then release a large quantity of water vapor, particularly when the HDD is operating under high temperature. The large quantity of water vapor released by the desiccant creates a high water vapor concentration within the HDD, which can cause severe reliability problems, such as lubricant pickup and loss of flying height for example.
To avoid this problem in manufacturing, the amount of time that the desiccant is exposed to the environment is tightly controlled. For example, desiccants may be kept in a dry environment until the last moment before they need to be installed into the HDD. As another example, the amount of time that an HDD is open and exposed to the outside environment may be minimized once the desiccant is installed. These strict procedures are detrimental to manufacturing flexibility and rework of the HDD.
When a HDD is stored for a long time under humid conditions, it is necessary to adjust the packaging of the HDD so that the packaging helps limit moisture intake. Desiccant packages in shipping boxes are also sometimes used, but their use is increasingly limited due to environmental concerns.